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Multiply a double-precision floating-point vector
xby a constantalpha.
npm install @stdlib/blas-base-dscalAlternatively,
- To load the package in a website via a
scripttag without installation and bundlers, use the ES Module available on theesmbranch (see README). - If you are using Deno, visit the
denobranch (see README for usage intructions). - For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the
umdbranch (see README).
The branches.md file summarizes the available branches and displays a diagram illustrating their relationships.
To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.
var dscal = require( '@stdlib/blas-base-dscal' );Multiplies a double-precision floating-point vector x by a constant alpha.
var Float64Array = require( '@stdlib/array-float64' );
var x = new Float64Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
dscal( x.length, 5.0, x, 1 );
// x => <Float64Array>[ -10.0, 5.0, 15.0, -25.0, 20.0, 0.0, -5.0, -15.0 ]The function has the following parameters:
- N: number of indexed elements.
- alpha: scalar constant.
- x: input
Float64Array. - stride: index increment.
The N and stride parameters determine which elements in x are accessed at runtime. For example, to multiply every other value by a constant
var Float64Array = require( '@stdlib/array-float64' );
var x = new Float64Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
dscal( 4, 5.0, x, 2 );
// x => <Float64Array>[ -10.0, 1.0, 15.0, -5.0, 20.0, 0.0, -5.0, -3.0 ]Note that indexing is relative to the first index. To introduce an offset, use typed array views.
var Float64Array = require( '@stdlib/array-float64' );
// Initial array...
var x0 = new Float64Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
// Create an offset view...
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
// Scale every other value...
dscal( 3, 5.0, x1, 2 );
// x0 => <Float64Array>[ 1.0, -10.0, 3.0, -20.0, 5.0, -30.0 ]If either N or stride is less than or equal to 0, the function returns x unchanged.
Multiplies a double-precision floating-point vector x by a constant alpha using alternative indexing semantics.
var Float64Array = require( '@stdlib/array-float64' );
var x = new Float64Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
dscal.ndarray( x.length, 5.0, x, 1, 0 );
// x => <Float64Array>[ -10.0, 5.0, 15.0, -25.0, 20.0, 0.0, -5.0, -15.0 ]The function has the following additional parameters:
- offset: starting index.
While typed array views mandate a view offset based on the underlying buffer, the offset parameter supports indexing semantics based on a starting index. For example, to multiply the last three elements of x by a constant
var Float64Array = require( '@stdlib/array-float64' );
var x = new Float64Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
dscal.ndarray( 3, 5.0, x, 1, x.length-3 );
// x => <Float64Array>[ 1.0, -2.0, 3.0, -20.0, 25.0, -30.0 ]var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var dscal = require( '@stdlib/blas-base-dscal' );
var opts = {
'dtype': 'float64'
};
var x = discreteUniform( 10, -100, 100, opts );
console.log( x );
dscal( x.length, 5.0, x, 1 );
console.log( x );#include "stdlib/blas/base/dscal.h"Multiplies each element of a double-precision floating-point vector by a constant.
const double x[] = { 1.0, 2.0, 3.0, 4.0 };
c_dscal( 4, 5.0, x, 1 );The function accepts the following arguments:
- N:
[in] CBLAS_INTnumber of indexed elements. - alpha:
[in] doublescalar constant. - X:
[inout] double*input array. - stride:
[in] CBLAS_INTindex increment forX.
void c_dscal( const CBLAS_INT N, const double alpha, double *X, const CBLAS_INT stride );#include "stdlib/blas/base/dscal.h"
#include <stdio.h>
int main( void ) {
// Create a strided array:
double x[] = { 1.0, -2.0, 3.0, -4.0, 5.0, -6.0, 7.0, -8.0 };
// Specify the number of elements:
const int N = 8;
// Specify a stride:
const int strideX = 1;
// Scale the vector:
c_dscal( N, 5.0, x, strideX );
// Print the result:
for ( int i = 0; i < 8; i++ ) {
printf( "x[ %i ] = %lf\n", i, x[ i ] );
}
}@stdlib/blas-base/daxpy: multiply a vector x by a constant and add the result to y.@stdlib/blas-base/gscal: multiply a vector by a constant.@stdlib/blas-base/sscal: multiply a single-precision floating-point vector by a constant.@stdlib/blas-base/saxpy: multiply a vector x by a constant and add the result to y.
This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.
For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.
See LICENSE.
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